Among the many DNA metabolic enzymes described in a wide range of organisms, deoxyribonucleases are central to a variety of biological functions. they are important in correcting errors in replication, processing naturally occuring and damage-induced lesions in DNA, and they are required for normal and induced recombination. They are presumed to function in the development of antibody diversity as part of recombination processes and they may be essential in apoptosis. The protein RhoNUC(y) was isolated initially as a nuclease from the yeast Saccharomyces cerevisiae and was subsequently shown to code for a chimeric protein with unique properties. This protein possesses features expected of both a DNA metabolic protein and a signal protein. The evidence to-date indicated that RhoNUC(y) may play a role in cell-signaling in response to DNA damage, cell growth and development and it can function in recombination. Utilizing antibodies raised against a portion of the RhoNUC(y) and antibodies against a related nuclease from Neurospora crassa, a related protein was isolated from monkey cells. The protein exhibited many nuclease features common to RhoNUC(y). A similar protein isolated with antibodies that react to RhoNUC(y) appears present in human cells. Given the importance of the yeast RhoNUC and demonstrated nuclease activity of the isolated monkey and human nuclease antigenic homologues, the human proteins are candidates for important DNA metabolic functions. The objectives of this project are to pursue the role of this protein(s) in human cells through a) the isolation and characterization of human RhoNUC(y) homologues, both proteins and corresponding genes, and the identification of associated proteins and genes; and b) the development of mutants in mammalian and human cells that are deficient in genes corresponding to the RhoNUC(Y) homologue and related genes.